Monday, May 1, 2017

Enumerating for Privilege Escalation: Linux

So, you have a shell on a Linux machine. But what now? Privilege Escalation! (Unless you spawned a root shell of course! Then its time for some lateral movement I suppose). But before you can escalate your privileges, you will have to figure out how you are going to do it. So that brings us to enumeration, which is hands down the most important part of compromising a target.

So this post is not intended to be a definitive guide to Linux priv-esc or anything, but merely a simple collection of things that I have personally found helpful during enumeration. I am totally open to suggestions or any ideas. This post is also heavily inspired by g0tmi1k's amazing post, Basic Linux Privilege Escalation:

I recommend bookmarking that ^

Get Your Bearings

First things first. Always get a good feel for the machine. Its always a good idea to figure out what version you're looking at:

cat /etc/issue

cat /etc/*-release

What is the kernel version? Are there known exploits for that version?

cat /proc/version
uname -a
rpm -q kernel

Where are you on the network? What connections are established? 

ifconfig -a
netstat -antup
iptables -L
arp -e

What is running?

There are numerous local privilege escalation exploits out there in the void. Are there any vulnerable applications or services running that have known exploits?

Which services are being run with root privileges?

ps -ef | grep root

ps aux | grep root 

cat /etc/services

Any vulnerable applications?

ls -alh /usr/bin/
ls -alh /sbin/

Any files with SUID/SGID permissions?

find / -perm -g=s -o -perm -u=s -type f 2>/dev/null
or, for a faster search in "bin" directories
for i in `locate -r "bin$"`; do find $i \( -perm -4000 -o -perm -2000 \) -type f 2>/dev/null; done

Uploading and running exploit code

If there is a local privilege escalation exploit available, how will you upload and execute the exploit code on your target? 

What languages are supported on the machine?

find / -name <language>*
ex: find / -name python*

Is GCC present?

find / -name gcc

How can you upload the exploit code? Use find to look for things like:

wget, nc, netcat, tftp, ftp, fetch etc.

Where can you write and execute files?

You will need to find a place to compile and execute your exploit code

This will locate world writeable and world executable folders

find / \(-perm -o w -perm -o x\) -type d 2>/dev/null 

Cracking passwords

Can you view /etc/passwd and /etc/shadow ?

cat /etc/passwd
cat /etc/shadow

If you can, try to crack the hashes you find. You never know!

Limited Shell?

Give these a shot.

python -c 'import pty;pty.spawn("/bin/bash")'
echo os.system('/bin/bash')

The simplest things are often overlooked

If I am ever stuck getting root privileges, its 9 times out of 10 because I am overthinking it. Sometimes the answer is so simple that its easy to overlook it. If you're getting stuck, think back to square one and move forward slowly and pay attention to the details. Here are some of simple things that can be overlooked:

Is the account you are using a sudoer? If you have the password for the account, you may be able to use sudo. I have seen many people look over this. Are there other users that are sudoers?

cat /etc/sudoers
sudo -l

Always check for password reuse. Unless of course you don't want to be noisy and risk a failed authentication.

Sometimes people don't think straight and put plain text passwords in .txt files and spreadsheets and all kinds of terribly insecure places, so don't disregard the idea. 

Enumeration scripts

To make life easier, you can write your own bash script to run whatever commands you want, although sometimes it is not plausible to do so. For example if you do not have the privilege to upload files or execute shell scripts. 

Anyways, those are my usual go-to commands when I start enumerating for priv-esc. It is not an exhaustive list by any means, there is a whole world of possibilities out there for getting root and hopefully this will help! I'm sure I will add things as I think of them, seeing as I wrote this on my lunch at work and probably forgot a bunch of stuff. Happy Hunting.

Thank you to g0tmi1k for your awesome post on the subject. I have used it more than any other blog I can think of!   

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